Bump tensorflow from 1.15.2 to 2.5.1

Bumps [tensorflow](https://github.com/tensorflow/tensorflow) from 1.15.2 to 2.5.1.
- [Release notes](https://github.com/tensorflow/tensorflow/releases)
- [Changelog](https://github.com/tensorflow/tensorflow/blob/master/RELEASE.md)
- [Commits](tensorflow/tensorflow@v1.15.2...v2.5.1)

---
updated-dependencies:
- dependency-name: tensorflow
  dependency-type: direct:production
...

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Author: dependabot[bot]

requirements.txt

@@ -1,6 +1,6 @@
 torch==1.0.1.post2
 torchtext==0.6.0
-tensorflow==1.15.2
+tensorflow==2.5.1
 Keras==2.0.0
 numpy==1.15.4
 pandas==1.0.3